Production of acrylates by catalytic dehydration of lactic acid and alkyl lactates



stead.

Unit d S 6 Pat PRODUCTION OF ACRYLATES BY CATALYTIC DEHYDRATION 0F LACTIC ACID AND ALKYL LACTATES No Drawing. Application January 12, 1956 Serial No. 558,607

4 Claims. (Cl. 260-486) This invention is concerned with the production of acrylates, including acrylic acid as well as its lower alkyl esters, from corresponding lactates by a direct catalytic process at an elevated temperature.

This application is a continuation-in-part of my co pending application Serial No. 319,185, filed November 6, 1952, now abandoned.-

The acrylates comprise a class of materials which are of great industrial importance due to their ability to form polymers and copolymers having a wide range of applications. The relatively high cost of the acrylates has, however, been a deterrent to their use in many applications for which their physical and chemical properties are well suited. The high cost of these materials has been in part a resultof the methods of preparation previously available, involving multiple-step processes, i significant yields to acrylate material by direct catalytic use of large amounts of auxiliary reagents, and other inefficiencies. The development of new and more efficient processes for the production of acrylates has therefore long been an objective of those working in this field.

The oxidation of acrolein by means of silver oxide was formerly employed in producing acrylic acid, from which other acrylates could then be obtained. The silver oxide reagent was expensive and was reduced to the metal during the reaction, requiring reconversion to silver oxide prior to re-use.

Hydrolysis of ethylene cyanhydrin or of acrylonitrile provides much of the acrylates now produced commercially. Neither intermediate is low in cost. Considerable quantities of acidic reagents are required.

Another method of preparation involves the pyrolysis of polymeric beta-lactone produced from ketene and formaldehyde' Several separate reactions'are involved, including lactone formation, polymerization, and pyroysis.

Acrylates have been synthesized from acetylene, carbon monoxide and water or alcohol; but this process has not achieved commercial importance. Recovery of expensive catalyst presents a major problem.

The dehydration'of hydracrylic acid (beta-hydroxypropionic acid) or alkyl esters thereof to the corresponding acrylate is a comparatively simple and economical process, but the starting materialis neither low in cost nor readily available in quantity. Alpha-hydroxypropionic acid (lactic acid) is much more readily and potentially available, but this material, as such, has never been found to be an effective source of acrylates.

When heated at moderate temperatures, lactic acid readily converts to polylactic acid or lactides. For example, Whitmore, Organic Chemistry, in discussing the preparation of acrylic acid, states: It is not obtained from lactic acid or its esters which give a lactide in- At higher temperatures, lactic acid and its esters have been shown by Net, and more recently by Fisher and Filachione of the U. S. Dept. of Agriculture, to de-' compose into acetaldehyde, carbon monoxide, and water r 2,859,240 Patented Nov. 4, 1958 or alcohol; a reaction which is typical of aliphatic alphahydro-alpha-hydroxy acids. This same decomposition to an aldehyde having one less carbon atom in the carbon chain is also typical of procedures known to the prior art in which lactic acid or the like is heated in the presence of strong acids such as sulfuric or phosphoric acid.

In view of such prior art experience, it isnot surprising that any methods for the preparation of acrylates based on lactic acid or its esters as a raw material have invariably involved the preliminary replacement of the alpha-hydroxy hydrogen (and the carboxyl hydrogen, when present) by some other radical whereby lactide formation and decomposition could be avoided, followed by pyrolysis of the substituted lactate to the acrylate. Typical of such methods is the acetylation of methyl lactate to methyl alpha-acetoxy propionate followed by pyrolysis to methyl acrylate and acetic acid.

Thus, despite the ready availability of lactic acid and the obvious advantages attendant upon its use, and further despite the very considerable efforts applied by researchers toward a solution of the problem, the'fact remains that no one, prior to the present invention, ever succeeded in directly converting lactates to acrylates. See, for example, the review 'by C. H. Fisher et al. entitled Properties and Reactions of Lactic Acid and published by the U. S. Dept. of Agriculture, No. A10- 279, October 1950.

It has now been discovered, contrary to all previous experience, that lactate material, i. e., lactic acid and the lower alkyl esters thereof, may be converted in dehydration at temperatures Within the range of about 200600 C., or more particularly at temperatures within' the more restricted and generally preferred range of about 250550 C. V

This is particularly surprising with respect to lactic acid itself. Atwood, in his Patent No. 2,464,364, for example, finds it necessary to remove all traces of lactic acid from his mixture of alkyl lactate and acetic anhydride in order to prevent excessive coke formation in the. pyrolyzing furnace.

Specific examples will now be set forth in further explanation, but with no intent of limitation, of the invention.

EXAMPLE 1 A catalyst was made by pelleting NaH PO .H O mixed with one-fourth its weight of graphite as a lubricant. Other lubricants, e. g., sodium stearate, are equally effective in providing coherent pellets. The amount of lubricant may be much less than here indicated.

A quantity of the catalyst pellets having an apparent volume of about 65 ml. was used to pack a- 10 section of a 1 /8" 0. D. Pyrex glass combustion tube passing through a Hoskins electrically heated tube furnace supported vertically. The furnace temperature .Was slowly raised so as to remove combined water without fusing the catalyst mass. A dropping funnel having provision for admitting inert gas and for pressure equalin sweeping the feed material and products through the train.

Methyl lactate was fed from the dropping funnel onto the dehydrated heated catalyst at a rate of about one drop per 4-5'seconds, and samples of the condensate were centigrade corresponding to the average recorded temperature.

The condensate contained methyl acrylate. After standing at room temperature for abouttwo weeks it was found that polymerization of the methyl acrylate had caused an increase in'the viscosity of the samples, particularly thosetaken at 510.532''C.

EXAMPLE 2 A 9 inch section of the combustion tube of the apparatus described in Example 1 was packed with 610 mesh granules of a catalyst material prepared by mixing a concentrated'solution of Na SO with finely divided CaSO in 'a 1:25 mol ratio to form a stiff paste which was dried in a thin-layer,brol en into small pieces, and screened. A short upper section of the combustion-tube was'fille'd with Pyrex glass helices-for preheating the feed. An aqueous 10% solution of lactic acid was fed into the tube at 1'0-1'5 ml. per. hour, the furnace temperature being 400 C. The condensate recovered was fractionated and an aqueous fraction was obtained' which on analysis was found to contain acrylic acid in an amount equal to 68% of'thecreticalbased on the amount of lactic acid employed.

EXAMPLE 3 EXAMPLE 4 Analytical'grade finely powdered'bariumsulfate was granulated by slurrying and drying, and a 9 inch section was employed in the combustion tube as the catalyst for pyrolysis ofmethyl'lactate. At 350" C. and a feed rate of 10-15 ml. per hour of the liquid ester, 28.4% of the ester was converted to methyl acrylate and 17.4% to acrylic acid, the total conversion thus being 45.8%.

EXAMPLE 5- An aqueous 50% solution'of lactic acid was converted to acrylicacid'in 50.7% yield by the action, at. a'furnace temperature of 425 C. and in the apparatus of Example 1,-of a granular catalystmixture'prepared from-c2180.; and Na P O in 25:1 mol ratio. Feed rate was 17.2 ml. per hour and the catalyst bed was 3 inches in length, with 'a short preheater section just preceding the catalyst.

EXAMPLE 6 Ethyl lactate was passed through the catalyst bed as in :Examplel. Theiurnace temperature was 454C. From .83 ml. of ethyl.lactate.there"was condensed 70 .g.r,of liquid in the water-cooled receiver. .A 37 g. portion of this was roughly fractionated to give 2.2 g. to 56 .C., 4.2 g. from 5076 C.,.9.9 g. from 7683 C., l g. from -.83-120 .0. .plus 19.2 g. residue. The fractions boiling ;from.5()-76 C..and.from 7 v683 C. were combined and to butene and acrylic acid.

redistilled. A portion weighing 6.8 g., boiling from 70-77 C., and containing chiefly ethanol and ethyl acrylate, began to show polymerization after a few hours in the sunlight. The slightly viscous liquid was allowed to evaporate, leaving afilm of clear polyethylacrylate. The identity of the polymer "was confirmed by infrared absorption analysis.

"EXAMPLE'7 In this experiment butyl lactate was passed over .a pelleted catalyst which was prepared, in accordance with the procedure described under 'Example'l, from lithium hydrogen phosphate mixed with some graphite. The furnace temperature was 510 C. From 14 ml. of butyl lactate there .was obtained 6.2 g. of nearly water-white pyrolysate. After adding a few granules of benzoyl peroxide and warmingfor thirty minutes on a water bath the acrylate in the pyrolysate polymerized to give a viscous liquid. The clear solid isolatedby evaporation of the volatile material was identified as chiefly polyacrylic acid, and'butene was identifiedjin the'residue recovered in the 'Dry=lce trap, indicatingthat :at the temperature used the butyl acrylate firstformed was further pyrolyzed EXAMPLE .;.8

In this experiment lactic-acid was directly dehydrated to acrylic acid. A solution of 70 ml. of"85%lactic acid in 30 ml. of watenwas passed at 482 C. furnace temperature over catalyst pellets: prepared,-as inExarnple '1,"from sodium dihydrogen phosphate mixed with one=fourthits Weight of I graphite =as a lubricant, and further treated by soaking in "a mixture-of 6 "mlaof 85% phosphorici'acid and 70 .ml. isopropanol for thirteen "minutes before dry ingfor use. From -'1'5'ml. of-feed was obtained 146g. pyrolysate in the water-cooled condenser. ThiswasdiS- tilled to give 10 g. -boilingto -100"C. and-4--g.-from 100-103 C. The latter fraction was found by'ultra violetabsorption analysis of a sample 'to contain about 39% of acrylic acid. This was further-demonstrated by adding to another sample a small amount of calcium carbonate followed by sodium sulfite and sodium persulfate. After a'short induct-ion period a precipitate of polymerized calcium acrylate appeared and coagulated to a sticky ball of polymer.

using methyl lactate :as 'thezfeedand a'catalyst prepared a by carefully heating;:a miXture-ofbarium hydrogen phosphate and. graphite. .At 454 :C.:-a 15%conversion of methyl lactateto methyl'acrylate was obtained, calculated from the ester content of'the product fraction boiling up to 70 C. a

The catalyst was prepared by first dissolving 395g.- of

BaCO in a mixture of 30,-ml. 'of water and 27.6 g. of i 85% H PO this productrwas mixed with 50 g. of

graphite and then dried,at, 125.C..before it was broken into small lumps and placed .in the reaction vtube 'for further heating.

EXAMPLE 10 A catalyst prepared by the method of, Example 9 from V 38.6 g. of tertiary zinc phosphate, 13.8 g. of 85% H l-"O and 40g. of graphite gave about a 7% conversion of methyl lactate to methyl acrylate at 454 C. furnace temperature.

EXAMPLE 11 Methyl lactate was passed over 'a catalyst made from about200 ndof granular bone charcoal which on analysis showed 81.8% ash 'and' which was treated with-5 "got H PO in ml. isopropanol'before drying "for use.

The bone charcoalcontained alarge amount 'of' ture of 343 C. a 20% conversion of the methyl lactate to methyl acrylate was effected as determined by the ester content of the product fraction.

EXAMPLE 12 be highly accurate in the absence of other low-boiling esters. In doubtful cases the results of the saponification test were further checked by means of ultraviolet ab-- sorption curves, and/or by iodine back-titration of do I decyl mercaptan added in excess, in accordance with the In this experiment methyl lactate Was passed over procedure described by Bessing et al., Anal. Chem., vol; silica gel WhlCh had been impregnated with about 35-40% 21, page 1073 (1949). Where the product comprises: by weight of monosodium phosphate and heated. At a acrylic acid, the quantity of this material is determined furnace temperature of 43 C. a 20% conversion to in known manner, e. g., by bromine addition after remethyl acrylate was obtained. As little as about 25% moval of other unsaturates. Acrylic acid has also been of the P 2 4 was q y efiectlvedetermined by ultraviolet absorption and by. solids deterwhenflsillica gel without the IIIOIIOSOdlUm phosphate i tien after polymerization. was sim' ar y tested as a catalyst, no significant yield of acrylate was obtained. V EXAMPLE 23 The following tabulation provides significant data on Butyl lactate was substituted for methyl lactate as the a number of additional experiments in which methyl feed, other conditions being the same as for Example 21, lactate was catalytically dehydrated in the absence of The distillate contained a mixture of butyl acrylate and oxygen 1n an apparatus as described under Example 1 acrylic acid which polymerized on standing. and at the furnace temperature indlcated. The catalyst EXAMPLE 24 in each case was prepared by combining the indicated com- I ponents and preliminarily heating the mixture slowly to Butyl lactate was also pyrolyzed by dispersing a the mdicated temperature 1n the Pyrex tube, any evolved powdered mixture of 6 grams of 'Na HPO and 4 grams of water'bemg removed from the system. The silica gel or MgSO; in '100 'ml. of Stanolind white mineral oil, heat. equivalent serves to increase the active surface area of ing themixture to' 350 C., and adding the butyl lactate the catalyst. V dropwise while maintaining the temperature and with Dehydration of Methyl Lactate f Furnace Example Catalyst Temper- Results ature,

l3 7 400 14% colnversion tomethyl BC 8t 4 I4 343 22% conversiontomethyl V acrylate. 343 15% couverslontomethyl --V-- acrylate. V r 16 V 532 9% conversion to methyl acry te. 17 l 400 more than 11% conver- Graphite-28 g; sion to methyl acrylate. 18 V NaHiPO4.HO on Darco Granules 427 23% colmtrersion tomethyl 80 p a e. NaH2PO4.HzO Q.5 mol .L'. W 19 {NQ2HPO4-0 5 mol f 482 17% conversion to methyl Graphite g acrylate. NaH2PO4.H208D g 20 {Graphite20 gu' 454 17% conversiontomethyl HQPO; to adjust pH to about 3.5 acrylate considerable acrylic acid (25% as determined by unsaturation). NaHzPO4.HzO10 g 21 {ggggg gg 270-343 10-13% convers on to (on commas-eats;singlets." methylactylate- 22 OaSO; (soluble anhydrite) 400 20% colngersiontomethyl 7 v acrya e.

Inthe above table, *Darco. and Columbia Carbon SXA are commercial varieties ,of, activated carbon analyzing, respectively, 19.7% and 0.9% ash. The silica gel produced a residue of 0.15% onevaporatibn with HF and H 80 These materials are employed as carriers for the alkali or alkaline earth phosphate or sulfate catalyst materials. .The Na WO included in thecatalyst of Example 21 is seen to decrease the yield of acrylate product. p 7

The percentage-conversion of methyl lactate 'to methyl acrylate, reported in the examples, unless otherwise in;- dicated was determined on the basis of the saponification equivalent The product from the catalytic dehydration was first distilled through an. unpacked column of about 1 2 inch length and about 6 mm. inside diameter. The fraction distilling at 85 0, containing the methyl 'acrylate together with a quantity of methanol, was treated with alcoholic KOH to 'saponify the acrylate. From the results thus obtained, the percent of the initial amount of methyl lactate which had been converted to methyl acrylate -was calculated. Th'emethod of analysis was checked by analysis of known mixtures of methyl acrylate, methyllactate and methyl alcohol and found to constant stirring. A portion of the distilled productboiling over the range of l40l50 C. contained acrylic acid which could be polymerized. The identity of the polymer was confirmed by infrared absorption analysis.

EXAMPLE 25 EXAMPLE 26 A catalyst mass was prepared bysoaking ml. of commercial 4-8 mesh activated alumina in 40 ml of an aqueous solution made from 27 grams of hydrous aluminum sulfate containing 27% water, and 20lgrams of magnesium sulfate, dissolved in ml. of distilled water,

and then carefully'drying; the treated granules tit/180" C.

'Lhecatalyst mass was placed in the reactor tube of Ex-:

ample 1 and ethyl lactate was introduced, together with nitrpgfin as, he inert carrier. The furnace temperature was held-at 300-360" C. The product was fractionated. The portion boiling at 54-88 C. contained ethyl acrylate, which polymerized on standing. The polymer was further identified by infrared, absorption analysis as polyethylacr-ylate. a e

. EXAMPLE 27 At a furnace temperature of 343 (3., methyl lactate was passed at-a feed rate of 0.30 ml; of liquid per ml. of catalyst per hour over a pelleted catalyst prepared from 50 grams of CaSO (soluble anhydrite) and 0.01 mol NaH PO .I-I O, in the presence of the customary inert atmosphere. Analysis of the fractionated product indicated a 5 conversion tomethyl acrylate and about 21% conversion to acrylic acid.

Calcium sulfate dihydrate (CaSO .2H O) may be used in place of the anhydrous material in preparing the catalyst mass.

EXAMPLE 28 In this'example the mol ratio of CaSO to NaH PO .H O in the catalyst mass was changed to 3:1. With the furnace at 371 C., a solution of methyl lactate in twice its weight of methanol was introduced, to provide a product fraction boiling at 5085 C. containing methyl acrylate in an amount representing at least about 40% conversion.

EXAMPLE 29 Methyl lactate was contacted with a pelleted catalyst prepared from sodium ferric pyrophosphate mixed with 2% of sodium stearate as a lubricant, stearic acid being removed during preliminary heating. The furnace temperature was 400 C. The conversion to methylacrylate was about 17% as determined by the saponification equivalent of the fraction boiling at 5085 C. On standing, the acrylate in this fraction polymerized to give a viscous solution of polymethylacrylate.

EXAMPLE 30 A catalyst mass was prepared by treating 50 grams a of silica gel with 0.02 mol of Na SO The mass was carefully heated in the apparatus of the preceding .examples. With the furnace at 343 0., methyl lactate.

was passed over the catalyst. Of the total amount in-' troduced, about 18% was converted to methyl acrylate and a considerable proportion was converted to acrylic acid, which was isolated in a fraction boiling at IDS-150 C. The acrylic acid, in the form of its calcium salt, readily polymerized when the solution was treated with Na s O NaI-ISO and CaCl and diluted 50100% by volume with water.

' EXAMPLE 31 Aqueous lactic acid of about 30% concentration was fed into the'apparatus of Example 1 containing in this case a pelleted catalyst prepared from 138 grams NaI-I PO .HO, 12 grams NH H PO and 37.5 grams graphite. The furnace temperature was about 532 C. A portion of the product was distilled and the, aqueous fraction boiling up to 100 .C. collected. This fraction contained acrylic acid. A portion was treated with N'a S O NaHSO and CaCl and produced in a few 8 EXAMPLE 32 Granules formed of a mixture of'tricalcium phosphate Ca (PO and sodium pyrophosphate'Na P O in;2-5,-:-1 molar ratio were employed as the catalyst mass. With the furnace at 425 C., an aqueous 50% solutionof lactic acid was converted to acrylic acid in 48-52% yield. The catalyst bed was 3 inches long and the feed rate was, about 31 ml. per hour.

In many of these examples the catalyst was used for long periods of time, both continuously and intermittently, with a continued high level of activity. Physical coating of the catalyst with polymeric products might be expected to occur,with resultant decrease in activity, in the, case, of extremely long runs; butno chemical deterioration has been observed. The action appears to be truly cata lytic. A physically coated catalyst may often be re generated by burning off the accumulated products ina stream of air at 400450 C.

In this connection, it will be appreciated that the cata-.

lyst as it is employed in the reaction is not necessarily in the same form, either chemically orphysically, as is the catalyst mass when first charged to the reactor. Many.

of the catalyst materials herein specified, particularly, such compounds as monosodium phosphate, disodium phosphate, primary calcium phosphate, etc. when heated are known to change to pyrophosphates, metaphosphates, polyphosphates or other modifications possessing improved stability at the temperature employed. These latter prod:

ucts which are considered as falling within the term. phosphates, act as true catalysts to promote a change V in the reacting materials without themselves undergoing any significant permanent change. 7

When a catalystmass is prepared by heating a com: pound or mixture which undergoes loss of water, care must be taken to prevent the solution or fusion of the mass in the process. For example, the transformation of; a sodium dihydrogen'phosphate to the metaphosphate requires slow and cautious heatingin order to obtain a. non-sintered catalyst mass having ,adequatesurface area...

Admixture with a relatively inert material such'as graphite V is sometimes of value in achieving a catalyst mass of suit able physical condition, as will be apparent from'several When mixed cataof the foregoing specific examples. lysts are used, care should be taken to avoid combinations which readily fuse at the operating temperatures employed or which react to result in a crystal structure altogether and unsuitably diiferent from that of the. original active components. 7

The rate of feed of the lactate material to the catalyst chamber is important ,in obtaining best results. Too'low.

a rate of feed is uneconomical, and too high a rate may result in ineflicient contactof the reactantwith the cat-' alyst mass. Thesurface area and activity 'of a particular catalyst will dictate the optimum feedrate for any given" temperature. With the apparatus described in Example '1 and the catalysts described in this specification, feed rates of about 0.060.35 ml. of liquid per ml. of catalyst per 1, hour have given good results, and these values will serve.

as a guide. For example, with concentrations of 0,025

0.05 and 0.1 mol of NaH PO on 50 grams of silicagel, feed rates of 0.066, 0.104 and 0.22 ml., respectively pro duced a 16-17% conversion of methyl lactate to methyl acrylate. However the invention is not to be considered .as restricted to these feed rates.

Below a furnace temperature of about 200 Cj.'little if any dehydration is accomplished. 'Above about 600"" (3.;

too much undesirable decomposition takes place. range of operating temperatures maybe expanded same;

what by judicious choice of catalysts and of operating; conditions,v but will serve to, establish a generally useful 1 range. Within the preferred range of about 2504550913,,

satisfactory rates of dehydration are obtained; with a;

minimumof undesirable .decompo'sitionyandlside reac;

tions. -With,the more active catalystsfternperatures npj' over about 400 C. are usually best, and when in addi-" tion highly porous supports such as silica gel areused, temperatures of around 300-345 C. are indicated. 'In, some cases the side reactions, while they unavoidably reduce the yield of acrylates, provide highly useful by-products. Thus in some instances there have been obtained small amounts of alpha, beta-dicarbonyl compounds, chiefly biacetyl, valuable as a flavoring and as a polymerization initiator, and capable of being condensed to form the polymerization inhibitor para-xyloquinone. However the production of acrylate material remains the chief result of the processes here described.

' The particular catalyst employed obviously has an efiect on the type and am ount of by-products formed. In general, it is found desirable to avoid catalysts having too low or too high a pH value, as well as those of pronounced oxidizing power, each of which tends to increase the proportion of side reactions ending in by-products, and/or to decrease the effective life of the catalyst. As an illustration, when a catalyst prepared from 0.01 mol NaH PO and 0.04 mol H PO (on 50 g. silica gel) was used, the conversion of methyl lactate to methyl acrylate fell to about /a of that obtained with NaH PO alone, and a considerable proportion of acetaldehyde was obtained. With Na PO alone, the conversion rate is fairly high, but condensation products are produced which contaminate the acrylate product unnecessarily and tend to cause premature loss of catalyst activity. The less soluble tribasic alkaline earth phosphates provide high yields and avoid the formation of large amounts of condensation products, as has been shown in Examples 3 and 32.

The proportion of undesired products produced in the reaction may be diminished in other ways also, e. g., by feeding such undesired materials with the lactate material into the reactor. For example, in the dehydration of methyl lactate, methanol may be added to suppress the hydrolysis of the ester. A mixture of methanol and lactic acid yields a product mixture of methyl acrylate and acrylic acid.

Other catalysts found to be active in converting lactate material to acrylate material by the procedures hereinbefore described have been prepared from the following compositions by heating to operating temperatures:

Ba P O +l% graphite (pelleted) CaI-IPO +10% graphite (pelleted) BaSO +10% graphite (pelleted) NaHSO on silica gel (0.01 M/50 g.) K 50 on silica'gel (0.03 M/50 g.)

Many other compounds which have been found useful in other applications as dehydration catalysts have been found to yield little or none of the desired product when employed as substitutes for the catalysts of the present invention. Thus, such materials as silico'phosphoric acid, phosphoric acid, pumice, W0 W 0 W 0 on Al, TiO Na WO Na MoO NaVO M003, Si O, A1203, NiMOO and ZnMoO although widely used in other dehydration processes, either fail to give any of the desired acrylate material when employed in connection with lactate starting materials, or give such a preponderance of contaminating by-products that their employment for the present purpose is totally impractical. I

As an illustration, the efiect of the incorporation of sodium molybdate in a typical catalyst mass will be described. Molybdates are often recommended as dehydrating catalysts for other processes. When methyl lactate was passed over a catalyst made in the manner hereinbefore described from 50 grams of silica gel, 0.04 mol NaH PO and 0.01 mol Na MoO about of the ester was converted to esters boiling below 85 C., and of these only about /5, i. e., only about 2% based on the lactate starting material, was the desired methyl acrylate.

, 10 t On the other hand, a catalyst produced from 50 grams silica gel and 0.05 mol NaH PO in the absence of molybdate, provided approximately a 19% conversion of the lactate to esters boiling below C., of which substantially the entire amount was methyl acrylate.

On the other hand, small amounts of various other ma terials may be incorporated with the catalyst materialto serve as promoters of the reaction. Lanthanumphosphate is one example of such a promoter; its eifect is illustrated in the following tabulation showing percent conversion of 50% lactic acid to acrylic acid with granular catalyst mixtures as defined and at 425 C.

Example I Catalyst Percent Conversion CaSOr-25 mols 54 C=H2P0rl moL- {C'aSO 25 mols--- 42 LaPOr-l mol In general, it is found that eifective results in terms of catalytic dehydration'of lactates to acrylates in accordance with the principles of this invention may be obtained by the use as catalysts of the sulfates and phosphates of metals of groups I and II of the periodic table which are at least as high as cadmium in the electromotive series. Of these, the salts of the alkaline earth metals, especially of calcium, strontium and barium, pro

vide the highest yields and are preferred. While the dehydration of lower alkyl lactates to corresponding acrylates is significant, the preparation of acrylic acid by direct catalytic dehydration of lactic acid is particularly important because of the greater economies in volved in the use of aqueous lactic acid solution. The latter preparation is also particularly unexpected in the light of prior art teachings such as found in Atwood Patent No. 2,464,364, as hereinbefore noted.

Thepractice of this invention is not limited to fixed bed catalysts, butmay be carried out with a fluidized bed when such conditions are advantageous. Similarly, variations in pressure from atmospheric to subatmospheric and to superatmospheric pressures are obvious extensions. Acid-resistant stainless steel reaction vessels may replace the Pyrex glass tube of the examples. Other non-inventive modifications will be apparent.

The isolation of pure acrylic acid or lower alkyl acrylates from the crude acrylate material obtained as the product of the novel process of this invention may be carried out by a combination of distillation and extraction or by any other suitable procedures. such as are already well known in the art.

What is claimed is as follows:

l. The process of catalytically producing acrylate material from lactate material which comprises the steps of (l) bringing volatile lactate starting material, having the formula CH CHOHCOOR, where R is selected from the group consisting of hydrogen, NH and alkyl containing l-4 carbon atoms, into contact with a dehydration catalyst consisting essentially of at least one member of the group consisting of the sulfates and phosphates of metals of groups I and II which are at' least as highas cadmium in the electromotive series, at a temperature within the range. of 200 C. to 600 C., and (2) separating acrylate material from at least some of the reaction products.

2. The process of catalytically'producing acrylates from lower alkyl esters of lactic acid which comprises the steps of (1) bringing a lower alkyl ester of lactic acid, wherein the alkyl radical contains 1%4 carbon atoms, into contact with a dehydration catalyst consisting essentially of at least one member of the group consisting of the sulfates and phosphates of metals of groups'I and II which are at least as high as cadmium in'theielectro "11 motive rseries, ,at .-a :ternperature within "the :range of 200.'C.1to 600 C., and;(2) separating acrylate;materia1 from at least some of a the reaction products.

3. The process of ;catalytical1y producing acrylic :acid from lactic acid whichcompri ses the stepsaof-(lybringing-lactic acidintocontact with a dehydration catalyst consisting .essentially :of .at least -,one member .of -the group consisting of the sulfates andphosphatesofimetals of groups I and II vwhich are at leastcashigh asgcadmium in theelectromotive: series, at a temperature :within the range of 200 ,C. to 600 C., and (2) Tseparating acrylic acid from at least some .ofltheoreaction products.

'4. The process of producing acrylates fromlactates which comprises directly catalytically dehydrating a lactate having the formula CH CHOHCOOR, by contact with a dehydration-catalyst consisting essentially of-at least one member of the group consisting of the sulof-thetc1ass consisting of hydrogen and lower alkyl radical containing .1-4 carbon atoms. 1

,References Citedjn the file of this patent umrEnesTATEs PATENTS 2,184,934 fBruson'et' al. 7 Dec. '26; 1939 "2,4281'673 -Miller, 'Qct. 7, '1947 i2;442,'716 weisberg-et'al. ....f1une 1, 1948, 2,464,364

Atwood MarglSQ 19149 v 

1. THE PROCESS OF CATALYTICALLY PRODUCING ACRYLATE MATERIAL FROM LACTATE MATERIAL WHICH COMPRISES THE STEPS OF (1) BRINGING VOLATILE LACTATE STARTING MATERIAL, HAVING THE FORMULA CH3CHOHCOOR, WHERE R IS SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, NH4 AND ALKYL CONTAINING 1-4 CARBON ATOMS, INTO CONTACT WITH A DEHYDRATION CATALYST CONSISTING ESSENTIALLY OF AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF THE SULFATES AND PHOSPHATE OF METALS OF GROUPS I AND II WHICH ARE AT LEAST AS HIGH AS CADMIUM IN THE ELECTROMOTIVE SERIES, AT A TEMPERATURE WITHIN THE RANGE OF 200*C. TO 600*C., AND (2) SEPARATING ACRYLATE MATERIAL FROM AT LEAST SOME OF THE REACTION PRODUCTS. 